Synthesis and Mössbauer Effect Study of Several Novel Bridged Derivatives of Me₂Si[(η⁵-C5H₄)₂Fe₂(CO)₄] and the Crystal Structure of Me₂Si[(η⁵-C5H₄)₂(CO)Fe(μ-CO)₂Fe(Ph₂PCH₂PPh₂)]


Irradiation of a benzene solution containing Me2Si[(η5-C5H4)Fe(CO) 2]2 (1) and either Ph2PCH2PPh2 or Ph2PCH2CH2PPh2 has led to the isolation of the monosubstituted complexes Me2Si[(η5-C5H4) 2(CO)Fe-(μ-CO)2Fe(Ph2P(CH2) nPPh2)], where n is one, 2a, or two, 2b. The key feature in these syntheses is the use of a 450-W medium-pressure Hg lamp which has lost a considerable amount of its intensity through at least 2000 h of use. The crystal and molecular structure of 2a has been determined by single-crystal X-ray diffraction. Complex 2a crystallizes in the space group P21/c with a = 12.389 (4) Å, b = 21.525 (7) Å, c = 13.507 (3) Å, and β = 91.81 (2)° with Z = 4. The structure is refined to R1 = 0.057 and R2 = 0.063 for 3270 independent reflections having I > 3σ(I). The Mössbauer effect spectra of 1 and 2 as well as of the complexes with intramolecular bidentate bis(phosphine) ligands, 3, and intermolecular bridging bis-(phosphine) ligands, 4, have been measured. The resulting spectra indicate only one iron site in 1, 3, and [(η5-C5H5)Fe(CO)2]2 (5) whereas two iron sites are observed in 2 and 4. The Me2Si bridge in 1 has little effect on the symmetry at the iron site as indicated by the similarity of its Mössbauer quadrupole splitting with that of 5. In addition, the average isomer shift increases upon phosphine substitution as a result of more extensive phosphine to iron π-bonding. The variation in the isomer shift in view of the almost constant iron-iron bond distance in these dimers provides further experimental support for the lack of direct iron-iron bonding in these compounds. © 1986 American Chemical Society.



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© 1986 American Chemical Society (ACS), All rights reserved.